Thermally coupled distillation systems (TCDS) have been proposed to perform distillation separation tasks with the incentive of achieving lower energy consumption levels with respect to conventional distillation sequences. Through the implementation of a vapor-liquid interconnection between two columns, a condenser or a reboiler of one of the columns is eliminated, and if a proper search on the operating conditions is performed, such an interconnection can provide energy savings (Hernández and Jiménez, 1999;Triantafyllou and Smith, 1992). TCDS for ternary mixtures have particularly been analyzed with special interest. Two of the schemes that have received special attention are systems with side columns (Finn, 1993;Hernández and Jiménez, 1996): the thermally coupled system with a side rectifier, TCDS-SR, and the coupled system with a side stripper, TCDS-SS. Those systems are shown in Figure 1.Many times, the design of integrated systems creates operational and control problems with respect to simpler designs. In particular, the presence of recycle streams for TCDS schemes has influenced the notion that control problems might be expected during the operation of those systems with respect to the rather well-known behavior of conventional distillation sequences. That has been one of the main reasons for the lack of industrial implementation of TCDS schemes. Recently, Agrawal (2000) proposed two arrangements that emerge from modifications to the systems shown in In this work we analyze the energy performance of the new arrangements and compare them to the behavior of the original integrated systems with side columns.
Design Method and Case StudiesFor the design of the TCDS arrangements, conventional sequences were first obtained (the direct sequence for the TCDS-SR, and the indirect sequence for the TCDS-SS). The sections performing similar tasks between the two types of systems were identified to produce the tray arrangement of the thermally coupled design. Such a design was then tested and optimized for energy consumption through rigorous simulations. Further details on the design procedure are given by Hernández and Jiménez (1996).The new schemes were then obtained directly from the TCDS arrangements following the simple tray section analogies depicted in Figures 1 and 2. The new systems were also subjected to an optimization procedure to detect the values of the side stream flow rates from the first column that minimized their energy consumptions. It should be noted that the range for the search procedure for these structures is more restricted than that for the TCDS structures because of mass balance considerations. The bounds for columns with side streams have been explained by Glinos and Malone (1985).To compare the behavior of the sequences with and without thermal coupling, three ternary mixtures with different values of the ease of separability index (ESI ϭ ␣ AB /␣ BC ), as defined by Tedder and Rudd (1978), were considered. A description of the mixtures is given in Table 1; the feed flow rate was 45.36
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.